The present invention relates to weighing vehicles and, in particular, it concerns a system and corresponding method for determining a total weight of a vehicle in motion.
Vehicle weight is known to be a key parameter in road safety. Overloading of vehicles is often responsible for braking failures as well as roll-overs. Overloading also frequently results in shortening of the mean time between failures (MTBF) of various vehicle subsystems, leading to system malfunction and vehicle failures which may lead to accidents. Overloading is also a major cause of damage to road infrastructure.
Although a weight limit is set for every vehicle, the limit is not always observed. Limits may be exceeded either as a result of miss-estimation of the weight loaded into a vehicle, or through intentional overloading to reduce transportation costs. Most commonly, vehicle weight is measured by use of external scales or weigh-bridges. Although there are checkpoints for weighing trucks, they are of limited effectiveness. Firstly, since the checkpoints are positioned in a limited number of locations, such as before certain bridges, they can only monitor a small proportion of the possibly overweight vehicles. Additionally, checkpoints are inefficient, requiring considerable staffing and wasting valuable transport time. Finally, a system of checkpoints cannot provide advanced warning to the operator of the vehicle when he begins a journey with an overloaded vehicle.
In the case of aircraft, overload may cause fatal accidents during take-off or on subsequent center-of-gravity shift. Monitoring the total load of an aircraft is currently done through summation of the weights of several partial loads. In other words, the various loads are added together, either manually or by computer, to estimate the sum total of the weight. As well as the possibility of faulty addition, errors may be introduced during estimation of the weight of the fuel added to the aircraft's tanks, or through error or omission in estimation of the initial weight prior to loading, for example, if some load has mistakenly not been removed from the aircraft.
A number of systems have been proposed for on-board weighing of loaded vehicles. U.S. Pat. Nos. 4,158,396 and 4,580,644 teach methods of weight estimation using load cells built into the suspension system of a vehicle. Such methods are intrusive, requiring redesigning of part of the vehicle structure and cannot typically be retrofitted. These systems are also only operative under static conditions. An alternative system disclosed in U.S. Pat. No. 5,410,109 requires installation of a piezo-resistive transducer sensor at each vehicle suspension point. This suffers from similar limitations of requiring design modification and only operating under static conditions.
U.S. Pat. No. 4,588,038 discloses a system which can also weigh during motion of the vehicle. The system calculates the weight on each axle by measuring the air pressure in suspension cylinders. Variations due to motion of the vehicle are eliminated by calculating an average value of the measured weight over a period of time. This system also requires adaptation of the existing vehicle systems, making retrofitting difficult.
There is therefore a need for a non-intrusive, retrofitable system and corresponding method for determining a total weight of a vehicle in motion.